1. Field of the Invention
The present invention relates to a circuit device and a method of manufacturing thereof, and specifically, relates to a circuit device of a size equal to a size of a circuit element and a method of manufacturing thereof.
2. Description of the Related Art
When electronic equipment such as mobile phones are miniaturized and sophisticated, circuit devices used in such equipment are also required to be further miniaturized.
A structure to package a highly-integrated circuit element has changed from a conventional QFP (Quad Flat Package) to a CSP (Chip Size Package). The CSP packages are formed by dicing a wafer which has external connection electrodes formed on a main surface thereof. Accordingly, each of the CSP packages is capable of being bonded to a mounting substrate with a size equal to that of the circuit element, and a side of the mounting substrate on which the CSP packages are mounted is capable of being miniaturized. Employing the CSP, therefore, enables an entire set of a mobile phone or the like to be miniaturized.
In the CSP, redistribution lines are formed on a main surface of the circuit element to redistribute electrodes of the circuit element. The electrodes of the circuit element are usually formed in a peripheral part of the circuit element which is not an area where integrated circuits are formed. A pitch between these electrodes is, for example, 70 μm and is very small, which makes solder connection difficult. The redistribution lines are therefore formed on the main surface of the circuit element in order to arrange external electrodes connected to the electrodes in a matrix. A pitch between the external electrodes is, for example, about 500 μm, which facilitates the solder connection.
With reference to FIG. 7, a description is given of a circuit device 100 of the conventional CSP type. The circuit device 100 includes an integrated circuit formed on a surface of a circuit element 101, and electrodes 104 which are connected to this integrated circuit are arranged in a peripheral part of the circuit device 100. The surface of the circuit element 101 is coated with a protection film 102 except in places where the electrodes 104 are exposed. The protection film 102 is a PSG (phospho-silicate-glass) film, a Si3N4 (silicon nitride) film, or the like.
Bumps 108 are formed on the respective electrodes 104 by a wire bonding technique and have a shape with an upper part constricted. Each of the bumps 108 is coated with a resin layer 103 except in an upper surface.
On an upper surface of the resin layer 103, redistribution lines 106 electrically connected to the respective bumps 108 are extended. Each redistribution line 106 is extended inward from the respective electrodes 104 located in the peripheral part of the circuit element 101. The redistribution lines 106 are coated with a resist 109 except in places where external electrodes 107 made of solder or the like are formed. This technology is described for instance in the Japanese Patent Application Publication No. Hei 9-64049.
However, in the aforementioned circuit device 100 of the conventional type, each path from the electrodes 104 to the respective redistribution lines 106 is made of different materials, thus causing a problem of poor joint reliability. Specifically, the bumps 108 were made of gold, copper, solder, or the like, and the redistribution lines 106 are generally made of copper. Therefore, the bumps 108 and the redistribution lines 106 are made of different materials in some cases, and thermal stress occurs in an interface therebetween following a change in temperature. Accordingly, disconnection may occur where the bumps 108 are joined with the respective redistribution lines 106. Furthermore, a shape of the bumps 108 is not a shape which is deformed following a thermal stress, which added to the problem.
Furthermore, because of the bumps 108, this conventional type is not capable of being applied to a miniaturized circuit element. A diameter of the bumps 108 formed by the wire bonding technique is about 30 to 60 μm, and the electrode 104 needed to be larger than that. Accordingly, there is a problem that the bumps 108 cannot be formed in a circuit element having minute electrodes with a side length of not more than 30 μm.
Still furthermore, there is a problem that forming the bumps 108 by the wire bonding technique increases manufacturing costs of the CSP.